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AuPdAlTi/AlGaN/GaN ohmic contact structures with varying Ti:Al ratios have been investigated. The relationship between Ti:Al ratio, interfacial microstructure, and contact resistance is examined. Rapid thermal annealing temperatures of 850 °C or higher are required to produce an ohmic contact with annealing at 950 °C producing the lowest contact resistance in the majority of samples. Samples annealed at 950 °C have been analyzed using complementary transmission electron microscopy and electrical characterization techniques. A thin Ti-nitride region is found to form at the contact/semiconductor interface in all samples. Ti-nitride inclusions through the AlGaN/GaN layer are also observed, surrounded by an Al/Au rich metallurgical barrier layer, with the size of the inclusions increasing with Ti content. The size of these inclusions does not have any clear effect on the electrical characteristics of the contacts at room temperature, but samples with fewer inclusions show superior electrical characteristics at high temperatures. [ABSTRACT FROM AUTHOR]

AuTiAlTi/AlGaN/GaN ohmic contact structures rapid thermal annealed at 650, 750, 850, and 950 °C have been analyzed using complementary transmission electron microscopy and electrical characterization techniques. The relationship between annealing temperature, interfacial microstructure, and contact resistance is examined. Annealing temperatures of 750 °C or higher are required to produce an ohmic contact. Contacts annealed at 750 and 850 °C show a planar interface between contact and the AlGaN layer, with minimal consumption of the AlGaN and the formation of a thin TiN interfacial layer. Annealing at 950 °C produces the lowest contact resistance, with a structure showing inclusions through the AlGaN/GaN layer. These inclusions are also shown to be a Ti-nitride, having an Al/Au-rich metallurgical barrier layer surrounding them. However, this metallurgical layer does not produce an electrical barrier. [ABSTRACT FROM AUTHOR]